Solid Phase Synthesis of a Functionalized Bis-Peptide Using …
Published 5/15/2012
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In JoVE (1)
Other Publications (6)
Articles by Long-Xi Yu in JoVE
A Protocol for Detecting and Scavenging Gas-phase Free Radicals in Mainstream Cigarette Smoke
1CDCF-AOX Lab, 2National Biomedical Center for Advanced ESR Technology (ACERT), Department of Chemistry and Chemical Biology, Cornell University
Spin-trapping ESR spectroscopy was used to study the effect of plant antioxidants lycopene, pycnogenol and grape seed extract on scavenging gas-phase free radicals in cigarette smoke.
Other articles by Long-Xi Yu on PubMed
Comparative Transcriptional Profiling of Placenta and Endosperm in Developing Maize Kernels in Response to Water Deficit
The early post-pollination phase of maize (Zea mays) development is particularly sensitive to water deficit stress. Using cDNA microarray, we studied transcriptional profiles of endosperm and placenta/pedicel tissues in developing maize kernels under water stress. At 9 d after pollination (DAP), placenta/pedicel and endosperm differed considerably in their transcriptional responses. In placenta/pedicel, 79 genes were significantly affected by stress and of these 89% were up-regulated, whereas in endosperm, 56 genes were significantly affected and 82% of these were down-regulated. Only nine of the stress-regulated genes were in common between these tissues. Hierarchical cluster analysis indicated that different sets of genes were regulated in the two tissues. After rewatering at 9 DAP, profiles at 12 DAP suggested that two regulons exist, one for genes responding specifically to concurrent imposition of stress, and another for genes remaining affected after transient stress. In placenta, genes encoding recognized stress tolerance proteins, including heat shock proteins, chaperonins, and major intrinsic proteins, were the largest class of genes regulated, all of which were up-regulated. In contrast, in endosperm, genes in the cell division and growth category represented a large class of down-regulated genes. Several cell wall-degrading enzymes were expressed at lower levels than in controls, suggesting that stress delayed normal advance to programmed cell death in the central endosperm. We suggest that the responsiveness of placenta to whole-plant stress factors (water potential, abscisic acid, and sugar flux) and of endosperm to indirect factors may play key roles in determining the threshold for kernel abortion.
Chilling Responses of Maize (Zea Mays L.) Seedlings: Root Hydraulic Conductance, Abscisic Acid, and Stomatal Conductance
Maize seedling water relations and abscisic acid (ABA) levels were measured over 24 h of root chilling (5.5 degrees C). At 2.5 h into chilling, leaf ABA levels increased by 40x and stomatal conductance (g(s)) decreased to 20% compared with prechill levels. Despite a rapid g(s) response to root chilling, leaf water potential (Psi(L)) of chilled seedlings decreased to -2.2 MPa resulting in a complete loss of turgor potential (psi(p)). Ineffective g(s) control early in chilling resulted from decreased root hydraulic conductance (L(r)) due to increased water viscosity and factor(s) intrinsic to the roots. After 24 h chilling, Psi(L) and psi(p) of chilled seedlings recovered to control levels due to stomatal control of transpiration and increased L(r). The impact of the temporal changes in g(s) and L(r) on maize seedling water relations during chilling was analysed using a simple, quantitative hydraulic model. It was determined that g(s) is critical to stabilizing Psi(L) at non-lethal levels in chilled seedlings at 2.5 h and 24 h chilling. However, there was also a significant contribution due to increased L(r) at 24 h chilling so that psi(p) increased to control levels. As a first step in determining the factor(s) responsible for the increase in L(r), cDNA microarrays were used to quantify the transcript levels of eight aquaporins obtained from mature root tissue at 24 h chilling. None of these were significantly up-regulated, suggesting that the increase in L(r) was not due to regulation of these aquaporins at the transcriptional level.
Expression of Thermostable Microbial Cellulases in the Chloroplasts of Nicotine-free Tobacco
An inexpensive source of active cellulases is critical to efficient and cost-effective conversion of lignocellulosic biomass to ethanol. Transgenic plants expressing foreign cellulases are potential sources of cellulases for biomass conversion. A number of foreign proteins have been reported to accumulate to high levels when the transgene is incorporated into the chloroplast genome rather than into the nuclear genome. We developed plastid transformation vectors carrying two Thermobifida fusca thermostable cellulases, Cel6A and Cel6B, and expressed them in nicotine-free or nicotine-containing tobacco varieties following chloroplast transformation. We obtained homoplasmic tobacco plants expressing Cel6A or Cel6B. Maximum estimates of expression levels ranged from 2 to 4% of total soluble protein. Enzyme assays indicated that both Cel6A and Cel6B expressed in transplastomic tobacco were active in hydrolyzing crystalline cellulose. With further optimization, it may be feasible to produce bacterial cellulases in tobacco chloroplasts in large quantities.
Diagnostic and Co-dominant PCR Markers for Wheat Stem Rust Resistance Genes Sr25 and Sr26
Wheat stem rust, caused by Puccinia graminis f. sp. tritici, is one of the most destructive diseases of wheat. A new race of the pathogen named TTKSK (syn. Ug99) and its derivatives detected in East Africa are virulent to many designated and undesignated stem rust resistance genes. The emergence and spread of those races pose an imminent threat to wheat production worldwide. Genes Sr25 and Sr26 transferred into wheat from Thinopyrum ponticum are effective against these new races. DNA markers for Sr25 and Sr26 are needed to pyramid both genes into adapted germplasm. The previously published dominant markers Gb for Sr25 and Sr26#43 for Sr26 were validated with eight wheat lines with or without Sr25 or Sr26. We tested six published STS (sequence tagged site) markers amplifying diagnostic bands of Th. ponticum. Marker BF145935 consistently amplified well and can be used as a co-dominant marker for Sr25. Among 16 STS markers developed from wheat ESTs mapped to deletion bin 6AL8-0.90-1.00, none was co-dominant for tagging Sr26. However, five 6A-specific markers were identified. Multiplex PCR with marker Sr26#43 and 6A-specific marker BE518379 can be used as a co-dominant marker for Sr26. The co-dominant markers for Sr25 and Sr26 were validated with 37 lines with known stem rust resistance genes. A diverse set of germplasm consisting 170 lines from CIMMYT, China, USA and other counties were screened with the co-dominant markers for Sr25 and Sr26. Five lines with the diagnostic fragment for Sr25 were identified, and they all have 'Wheatear' in their pedigrees, which is known to carry Sr25. None of the 170 lines tested had Sr26, as expected.
Effects of Root and Stem Extracts of Asparagus Cochinchinensis on Biochemical Indicators Related to Aging in the Brain and Liver of Mice
Asparagus cochinchinensis is a traditional Chinese medicine used for treating lung and spleen-related diseases. In this study, we compared the medicinal effects of A. cochinchinensis root and stem extracts on the activity of superoxide dismutase (SOD), the content of malonaldehyde (MDA) and total protein content in the brain, liver and plasma of mice. Polysaccharides and aqueous extracts of the roots significantly increased the spleen index and the SOD activity but reduced the MDA content and slowed down the aging process. In contrast, feeding with the stem extracts significantly reduced the SOD activity and increased the MDA accumulation in the brain and liver of mice, suggesting that the stem extracts may not be appropriate for treating aging-related diseases.
Association Mapping and Gene-gene Interaction for Stem Rust Resistance in CIMMYT Spring Wheat Germplasm
The recent emergence of wheat stem rust Ug99 and evolution of new races within the lineage threatens global wheat production because they overcome widely deployed stem rust resistance (Sr) genes that had been effective for many years. To identify loci conferring adult plant resistance to races of Ug99 in wheat, we employed an association mapping approach for 276 current spring wheat breeding lines from the International Maize and Wheat Improvement Center (CIMMYT). Breeding lines were genotyped with Diversity Array Technology (DArT) and microsatellite markers. Phenotypic data was collected on these lines for stem rust race Ug99 resistance at the adult plant stage in the stem rust resistance screening nursery in Njoro, Kenya in seasons 2008, 2009 and 2010. Fifteen marker loci were found to be significantly associated with stem rust resistance. Several markers appeared to be linked to known Sr genes, while other significant markers were located in chromosome regions where no Sr genes have been previously reported. Most of these new loci colocalized with QTLs identified recently in different biparental populations. Using the same data and Q + K covariate matrices, we investigated the interactions among marker loci using linear regression models to calculate P values for pairwise marker interactions. Resistance marker loci including the Sr2 locus on 3BS and the wPt1859 locus on 7DL had significant interaction effects with other loci in the same chromosome arm and with markers on chromosome 6B. Other resistance marker loci had significant pairwise interactions with markers on different chromosomes. Based on these results, we propose that a complex network of gene-gene interactions is, in part, responsible for resistance to Ug99. Further investigation may provide insight for understanding mechanisms that contribute to this resistance gene network.